1. Field of the Invention
The invention relates to a control device and control method for a vehicle, which execute hill hold control for applying braking force to wheels independent of driver's brake operation in response to an idling stop of an engine.
2. Description of Related Art
In a vehicle that is configured to couple an engine to a transmission via a fluid coupling, such as a torque converter, a set torque is applied to wheels due to creep torque even during idling of the engine. Therefore, in such a vehicle, even when a brake pedal is not depressed, it is possible to hold the vehicle in a stopped state on a hill by torque transmitted to wheels, that is, so-called creep torque, so a hill start of the vehicle is easy.
On the other hand, in recent years, for the purpose of improvement in fuel economy, there has been practically used a vehicle that performs idling stop in which engine operation is automatically stopped during a stop of the vehicle. In such a vehicle, when idling stop is performed during a stop of the vehicle on a hill, creep torque is not generated, and wheels are not braked during a pedal change operation from a brake pedal to an accelerator pedal, so the hill start performance of the vehicle deteriorates.
Then, in an existing art, Japanese Patent Application Publication No. 2000-313253 (JP 2000-313253 A) describes a control device for a vehicle. The control device executes hill hold control for applying braking force to wheels independent of driver's brake operation in response to an idling stop of an engine. By so doing, even when a brake pedal is released during a stop of the engine resulting from idling stop while the vehicle is stopped on a hill, the vehicle is maintained in a stopped state to allow easy hill start. Note that, in the control device for a vehicle, described in JP 2000-313253 A, hill hold control is cancelled on the condition that, after a command to restart the engine through cancellation of idling stop, an engine rotation speed is higher than or equal to a rotation speed at which it is possible to generate sufficient creep torque.
Incidentally, depending on circumstances, in process of stopping the engine through idling stop, that is, during coasting of the engine after operation of the engine is stopped, a command to restart the engine may be issued in response to driver's accelerator operation, or the like. In such a case as well, with the above described control device for a vehicle, when the engine rotation speed at the time of issuance of a restart command is sufficiently high, hill hold control is cancelled at that point in time. However, the engine rotation speed, at which it is possible to restart the engine with the use of a starter, has an upper limit, and a restart of the engine by driving the starter in response to a restart command cannot be performed until the engine rotation speed is sufficiently low. Therefore, in the above described case, the engine rotation speed decreases after cancellation of hill hold control and then sufficient creep torque may not be transmitted to the wheels. Then, in such a case, the wheels cannot be braked during a change operation from the brake pedal to the accelerator pedal, so the hill start performance of the vehicle deteriorates.
In addition, in process of stopping the engine through idling stop, a restart of the engine may not be initiated immediately after issuance of a restart command, so there occurs a delay from depression of the accelerator pedal to generation of propelling force of the vehicle. Therefore, when hill hold control is cancelled in process of stopping the engine through idling stop, even when a change operation from the brake pedal to the accelerator pedal is quickly performed, the vehicle cannot temporarily be held in a stopped state, so the hill start performance of the vehicle may deteriorate.